The present invention relates generally to a method and apparatus for the manufacture of boxes or cartons, and more specifically to a vision inspection or monitoring system for measuring in-line the quality of each finished box or carton--especially corrugated boxes.
Boxes or cartons such as corrugated boxes are produced by the container industry on high-speed manufacturing machinery. The machines employed for this purpose are complicated assemblages of interworking parts, which automate the box manufacturing process, converting a simple cardboard blank into a box in a "folded-down" state. In a typical process, score lines are added to the blank at appropriate positions in order to define four side panels and eight end panels. A glue flap extends along one of the side panels. The scored blank is fed to an automated machine, which employs a conveyor system to move the scored blank through the machine. In this way, the blank undergoes controlled movement in a longitudinal direction while minimizing and, preferably, eliminating undesirable lateral movement. Glue is applied to the glue flap at a "glue station" within the machine, and the exterior side panels of the blank are then folded upon their adjacent interior side panels by means of cooperating deflection devices provided along the conveyor belt path so that the glue flaps meet the opposite exterior panels in order to produce a finished box in its folded-down state, as it emerges from the machine. In an embodiment of this invention, the seam between the panel and the glue flap may be pressed through press rolls.
These boxes are manufactured at speeds in excess of 300 blanks per minute. Yet, at least thirty different machine variables such as feed roll pressure, conveyor belt speed, timing of the folding device cycle, and the like contribute to a properly manufactured box. For instance, if the folding mechanism is not timed properly in sequence with the moving blank, a square fold will not be obtained. Likewise, if the blank is not securely retained by the traveling or conveyor mechanism or is engaged too strongly by the folding mechanism, it could "fishtail," thereby preventing a square fold. Therefore, if any of these variables is not precisely coordinated with the other variables, the folding machine will not produce an optimal "square" box which, when unfolded, will have all 90.degree. angles.
The operator of the folding machine, thus, encounters significant problems in controlling the production of the boxes to achieve desired optimal results. Because the blanks travel at speeds in excess of 300 units per minute, it is impractical for the operator to visually follow the folding and gluing steps in order to control the process to produce boxes with 90.degree. angles. Likewise, it would be commercially unfeasible for the operator to cease operation of the folding machine periodically in order to inspect a box. Statistical processing control has been suggested to overcome this problem whereby selected representative samples of completed boxes are collected and analyzed to determine the acceptability of the product being produced and the desirability of adjusting the manufacturing process variables to overcome any detected defects. However, it is clear that an in-line capability of performing quality control checks of the product being produced without interfering with the production run would be highly desirable and significantly more operationally effective for adjustment of the process variables as opposed to analysis of already produced product. Also, quality control inspection of every box produced would be a highly desirable improvement over prior random sampling systems. Therefore, provision of such capability for in-line quality control monitoring of each box in production without interfering with the production run would be highly advantageous relative to prior processes employed in this art.
Various video inspection systems are known in the prior art. U.S. Pat. No. 4,344,146 issued to Davis, Jr. et al., for example, discloses such a scheme consisting of a television camera, which produces a digital video image of the subject matter, an interface with a direct memory access channel for structuring the digital data, high-speed random access memory for storing the data, a bus oriented processor for processing the data in the memory, a digital computer for controlling operation of the system, and a terminal which presents the data to the machine operator so any flawed work pieces may be detected and fixed. Davis indicates that such a system could be used to ensure that labels are correctly placed on bottles. U.S. Pat. No. 4,758,888 issued to Lapidot teaches an automatic work station for inspection of work pieces traveling along a production line, incorporating a television camera and a computer. The machine operation may retrieve the stored images to verify the detected flaws, and remove the applicable work pieces at a downstream sorting station. However, the video inspection systems disclosed by Davis and Lapidot merely provide a visual image of the workpiece, which then must be analyzed by the operator to determine whether any product flaws fall within acceptable ranges. Such an analysis is time consuming, prone to inaccuracy and subject to the skill of the operator.
U.S. Pat. No. 4,578,052 issued to Engel et al., by contrast, provides a method and apparatus for detecting deviations of folds in a sheet of paper in which electro-optical sensors are positioned above the folding cylinder of a folding machine. These sensors electrically evaluate markings prepositioned on the sheet along the desired fold line, and a computer evaluates and processes the data. As illustrated in FIG. 4 of the reference, the system detects sheets having skewed folds, because the distance between each respective mark and a common reference point will not be the same. The operator uses the data to make necessary adjustments to the folding machine. The Engel system, though, is dependent upon prepositioning the marks along the fold lines, which requires an extra step in the manufacturing process, thereby increasing production costs.